1. Field of the invention.
The present invention relates to RF sealers and, more particularly, to annular sealing devices.
2. Description of the prior art.
Heat weldable plastics have been commercially available for many years. Such plastics are generally welded to one another by applying a heater or heated element to the plastic with simultaneous compression against a base or anvil. By correctly guaging the proper combination of compressive force and heat applied, a weld can be made which will not melt the plastic sufficiently to affect its integrity nor preclude a proper weld from being formed. Because traditional heating elements tend to heat slowly and radiate heat during periods of use and nonuse as power is consumed to maintain the heating element at a predetermined temperature during periods of nonuse, alternative devices for forming the welds are preferable. The transmission of a burst of radio frequency (RF) energy across a junction of certain heat weldable plastic materials with the proper dielectric characteristics will heat such materials to a temperature sufficient to develop a weld therebetween. By combining a compressive or retaining force to the plastic junction at the time the RF energy is transmitted thereacross, a localized, well defined and high integrity weld can be made.
In the field of blood collection, tubes extending from and in fluid communication with filled blood collection bags must be sealed after fill of the bag. Such sealing can be effected in a number of ways U.S. Pat. No. 4,013,860, which patent is assigned to the present assignee, describes and illustrates a hand-held sealer for making welds across a length of plastic tubing. The sealer includes fixed and moveable jaws and a circuit for transmitting a particularly timed and configured pulse of RF energy across the moveable jaws after they have compressed to a predetermined extent the tubing to be sealed. The mechanical configuration, circuit and operation there of described and illustrated in this patent is incorporated herein by reference. U.S. Pat. No. 4,186,292, which patent is assigned to the present assignee, describes and illustrates a stationary sealer for sealing plastic tubing. Upon actuation of the sealer, the tubing is compressed whereafter a predetermined burst of RF energy is applied across the tubing to create a weld thereacross. The disclosure contained in this patent is incorporated herein by reference. U.S. Pat. No. 4,490,598, assigned to the present assignee, is directed to a particularly configured head for forming a weld across a length of plastic tubing in response to application of a compressive force and a burst of RF energy. The teachings contained therein are incorporated by reference in the present disclosure. U.S. Pat. No. 4,390,832, is directed to a circuit for providing a source of RF energy to be applied across a pair of jaws, or electrodes, to form a weld in weldable plastic material placed therebetween. In addition, numerous differently configured jaws for compressing or retaining the weldable plastic material placed therebetween and for focusing the applied burst of RF energy are disclosed. The teachings contained in this patent are incorporated herein by reference.
It is believed that the above referenced United States patents describe the state of the art in using RF energy to form welds across fluid filled or unfilled weldable plastic tubing. It is appreciated that various other types of welding apparatus using non RF heaters are known and used for the purpose of sealing packages, forming elongated welds in sheets of plastic and the like. However, such prior art is neither pertinent to or demonstrative of devices for meeting and resolving unique problems attendant the formation of seals in filled or unfilled weldable plastic tubing in response to a burst of RF energy.
To the knowledge of the present inventors, there are no devices commercially available nor any teachings for construction of a device which is capable of forming an annular weld between two concentric overlapping segments of weldable plastic by application of RF energy.